X-ray radiography, the taking of photographs by a form of radiation other than light (more specifically X-rays) is a useful medical diagnostic and therapeutic technique. At the same time such radiation used for radiography must be carefully controlled and limited to that necessary, particularly when X-rays are utilized for the treatment of human beings. The Bureau of Radiological Health (BRH) has promulgated Federal Regulations governing the performance of equipment utilized for such purposes.
In the past, attempts to refine the design of X-ray apparatus have resulted in the development of systems utilizing visible light beams to simulate and correspond to the coverage of the invisible X-ray beam so as to enable proper placement and coverage during X-ray radiography to comply with BRH regulations.
Attemps have been made in the past to provide an aid in aligning the film with the X-ray beam by having an optical system project two beams of light to aid in aligning film with the X-ray beam. The first beam of light, called a light localizer, corresponds in cross-sectional area in the film plane with the cross-sectional area of the invisible X-ray beam. Furthermore, to comply with BRH regulations, the X-ray beam cross-sectional area cannot overlap beyond the film area. The second visible light beam utilized in the past consisted of a relatively short line or stripe of light directed to an index mark on the handle of the X-ray film cassette tray. Because of the short length of this beam, it was found necessary to position the X-ray head at a fixed distance from the film in order for the beam to strike the indicator. This has been found to be a hindrance to the flexibility and speed and ease of operation of X-ray equipment.